Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$71.64	6.228%	$76.1017	$76.10	$76.10	$76.10
Purchase #2	$96.89	4.466%	$101.2171	$101.22	$101.20	$101.20
Purchase #3	$101.62	7.177%	$108.9133	$108.91	$108.90	$108.90
Purchase #4	$160.76	13.250%	$182.0607	$182.06	$182.05	$182.10
Purchase #5	$38.86	12.645%	$43.7738	$43.77	$43.75	$43.80
Purchase #6	$40.35	7.222%	$43.2641	$43.26	$43.25	$43.30
Purchase #7	$250.34	9.815%	$274.9109	$274.91	$274.90	$274.90
7 purchase totals =	$760.46		$830.2416	$830.23	$830.15	$830.30